FIG. 1 shows a single-pole multi-throw switch according to prior art. The single-pole multi-throw switch 100 includes four selection circuits 1101 to 1104 and the single-pole multi-throw switch 100 can transmit or receive signals required by the system by turning on one selection circuit among the four selection circuits 1101 to 1104. For example, when the single-pole multi-throw switch 100 is applied to a wireless communication system, the four selection circuits 1101 to 1104 can be coupled to different wireless communication modules 1301 to 1304 respectively so the single-pole multi-throw switch 100 can be used to transmit radio frequency signals to the related wireless communication module.
Each of the selection circuits 1101 to 1104 includes a plurality of selection transistors 120. When the system uses the single-pole multi-throw switch 100 to transmit signals, only one selection circuit is turned on. For example, when the system uses the single-pole multi-throw switch 100 and the wireless communication module 1301 to transmit signals, the selection transistors 120 of the selection circuit 1101 are turned on, and the selection transistors 120 of the other selection circuits 1102 to 1104 are all turned off. Each of the selection circuits 1102 to 1104 includes 14 selection transistors 120. If the effective capacitance of each of the selection transistors 120 is C, then the effective capacitance of the selection circuit 1102 will be the effective capacitance of 14 selection transistors 120 coupled in series, that is C/14, and the effective capacitance of the selection circuits 1102-1104 will be 3 C/14. Namely, when the system uses the selection circuit 1101 to transmit signals, the effective capacitance of turned-off transistors of the selection circuits 1102 to 1104 is the parasitic capacitance and excessive parasitic capacitance can weaken the strength of the transmission signals. In addition, the selection circuits 1102-1104 may require a significant size of area, which can be in conflict with the needs of mobile electronic devices.
Moreover, when the single-pole multi-throw switch 100 includes even more selection circuits, the required area will also increase. For example, according to the structure of the single-pole multi-throw switch 100 in FIG. 1, the size of area may increase significantly when the single-pole multi-throw switch 100 is expanded to include eight selection circuits. Therefore, how to reduce the parasitic capacitance and the required area of the single-pole multi-throw switch has become a critical issue to be solved.